1. Field of the Invention
The application relates to a method and a related communication device used in a wireless communication system and related communication device, and more particularly, to a method of applying discontinuous reception (DRX) operation and a related communication device in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as to user equipments (UEs).
A long term evolution-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system, considering relaying for cost-effective throughput enhancement and coverage extension. The LTE-A system includes all of the features of the LTE system and several new ones, the most important of which are: carrier aggregation (CA), enhanced multi-antenna support and relaying. The LTE system provides extensive support for deployment in spectrum allocations of various characteristics, with transmission bandwidths ranging from 1.4 MHz up to 20 MHz. In the LTE-A system, the transmission bandwidth can be further extended with carrier aggregation wherein multiple component carriers are aggregated and jointly used for transmission to/from a signal UE. In general, up to five component carriers can be aggregated, allowing for transmission bandwidth up to 100 MHz.
When CA is configured, the UE only has one RRC connection with the network. At RRC connection establishment/re-establishment, one serving cell provides the security input (one ECGI, one PCI and one ARFCN) and the NAS mobility information (e.g. TAI) similarly as in Rel-8/9 under 3GPP. This cell is referred to as the Primary serving cell (PCell). In the downlink, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DL PCC) while in the uplink it is the Uplink Primary Component Carrier (UL PCC). Depending on UE capabilities, Secondary serving cells (SCells) can be configured to form together with the PCell a set of serving cells. In the downlink, the carrier corresponding to an SCell is a Downlink Secondary Component Carrier (DL SCC) while in the uplink it is an Uplink Secondary Component Carrier (UL SCC). The configured set of serving cells for a UE therefore always consists of one PCell and one or more SCells.
According to the structure of LTE/LTE-A system, Discontinuous Reception (DRX) is applied to a MAC (Media Access Control) layer for allowing UE to enter a standby mode during certain periods and stopping monitoring a Physical down Link Control Channel (PDCCH) carrying information about resource allocation of a DL-SCH (Downlink Shared Channel) and uplink (UL) scheduling grants. The DRX functionality is operated based on the following parameters that can be configured by a DRX-configuration information element (IE) of a RRC (radio resource control) layer. The related DRX parameters include:
A DRX Cycle providing a periodic repetition of a “On Duration” followed by a possible inactivity period, where the DRX Cycle is a short or a long DRX cycle;
A DRX Inactivity Timer providing the number of consecutive PDCCH-subframe(s) after successfully decoding a PDCCH indicating an initial UL/DL user data transmission;
A DRX Retransmission Timer providing the maximum number of consecutive PDCCH-subframe(s) as soon as a DL retransmission is expected by the UE;
A DRX Short Cycle Timer providing the number of consecutive subframe(s) during which the UE shall follow the short DRX cycle after the DRX Inactivity Timer has expired;
A HARQ RTT Timer providing the minimum amount of subframe(s) before a DL HARQ retransmission is expected by the UE; and
An On Duration Timer providing the number of consecutive PDCCH-subframe(s) at the beginning of a DRX Cycle. The UE monitors the PDCCH only during the On Duration.
In Rel-10 of 3GPP, the UE applies a same DRX operation to a PCell and all activated SCells in carrier aggregation. The UE is configured with a PCell and a deactivated SCell. Once drx-InactivityTimer expires or a DRX Command MAC control element is received, the UE applies the DRX operation to the PCell and the SCell is still deactivated (i.e. the UE didn't apply the DRX to the deactivated SCell on that time). After that, the UE receives a Activation/Deactivation MAC CE activating the SCell and the SCell is activated. However the UE may not apply the DRX operation to the SCell and continue to receive a PDCCH on the SCell on an off duration in the DRX operation. This wastes UE power.